The present invention relates to a looper threading apparatus for a sewing machine for threading for a thread hole provided on a looper to be swung in order to form a stitch in cooperation with the needle of the sewing machine.
Conventionally, an overcasting overlock sewing machine and a multi-thread chain stitch sewing machine comprise a looper for reciprocating while drawing an arcuate track to cross the track of a needle according to the vertical motion of the needle. A looper thread led by the looper forms a stitch together with a needle thread.
Threading for the looper is usually carried out manually by using a pair of tweezers. A thread hole formed on the looper is small. Therefore, a threading work imposes a burden, on an operator, and a working efficiency is not always high.
In recent years, in order to enhance the efficiency of the threading work for a looper, a looper threading apparatus for carrying out threading by utilizing an air flow has been developed as described in JP-A-06-277383 (Japanese Patent Application Publication Number: Hei06-277383), for example.
The looper threading apparatus has a special structure that a looper is pipe-shaped, and furthermore, a pipe-shaped component to be a passage for an air flow and a thread passage is provided, and the pipe-shaped structure is caused to pass by the air flow to guide a looper thread into the tube of the tubular looper and to cause the looper thread to the outlet of the tip of the looper when the looper thread is inserted from one of the ends of the pipe-shaped structure.
In the looper threading apparatus described in JP-A-06-277383, however, in some cases in which a foreign substance such as machine oil, a waste thread or dust enters a thread passage having a hollow structure, the inner portion of a pipe is clogged up and stagnated. Consequently, a predetermined air flow for leading out the thread cannot be obtained. As a result, there is a problem in that the thread cannot pass so that threading cannot be carried out or the foreign substance is stuck to the thread to be contaminated in the pipe.
While a thread guide and a thread tensioner are usually provided in the thread passage of the looper thread to influence a thread tension, furthermore, there is a problem in that the thread tension is affected so that a proper thread tension cannot be obtained and the quality of a sewn product is thereby deteriorated when the foreign substance is present in the pipe as described above.
Moreover, there is a problem in that a complicated work for removing these foreign substances from the inner part of the pipe and cleaning the dirty inner part of the pipe is required and a working efficiency is deteriorated.